Tension Elements. 579 Advantages. 6. BELT GEARING. Disadvantages. Useful in connection with shafting as a distributor and modifier with comparatively few parts. Easily started and stopped. Practically noiseless. Very convenient for bridging rea- sonable distances. Large pull on bearings, but in well- lubricated bearings friction does not depend on pressure. Slip an advantage in case of shock. Frictional loss principally in the line shafting: about 257,, to 50% in a shop system. Large belts with heavy pressures are expensive to maintain. Slip a disadvantage where exact velocity ratio is required. 7. COTTON-ROPE GEARING. For fairly long-distance driving in mills, and for travelling cranes. Better grip than belts, due to wedge- groove pulleys. Quite noiseless. Separate driving to the various floors of a mill occasions less loss of time in breakdowns. Small liability to break down also. Frictional and other losses probably somewhat larger than with belt gear- ing, due to heavy pullies and fly- wheels. Working speeds being high, rope tension is increased 5o°/0 by centri- fugal force : but bearing pressures are not thereby affected. 8. WIRE-ROPE GEARING. Suitable for very long distances, say for several miles, when relays are adopted. Cases quoted in text. If moderate speeds be employed, little increased tension from centri- fugal force. Frictional and other losses 22S/0 per mile, not including motor and machines: lesser and greater distances in proportion. 9. PITCH-CHAIN GEARING. As useful as belt driving in de- creasing the number of parts while modifying the power: but gives at the same time positive transmission, and may be used with heavy loads. Adapted for high as well as low speeds if well made, but the former should go with light pressures. Frictional loss depends very much on design and manufacture, and pro- bably varies from 5% to 3O°/0 in a pair of wheels: there being two sets of friction surfaces, not including the journals. Increase of pitch after wear causes excessive friction and bad working.